This invention relates to railway tank cars, and more particularly to such tank cars which utilize a discharge valve located in the bottom of the tank car, with the discharge valve being selectively opened and closed by an outside unloading device or nozzle located on the top of the car above the bottom valve. Typically, the outside unloading device is operated by an attendant standing on a platform mounted on the top of the car.
More specifically, the outlet valve located in the car bottom may be any of a variety of known types of valves. Generally, however, these bottom mounted discharge valves operated by an outside unloading device requires rotation of a valve member in one direction or the other about a generally vertical axis so as to effect opening and closing of the valve. The valve member in the valve is connected to the outside unloading device located on the top of the car by means of an operating rod secured to the valve member, typically by a U-joint swivel connection, and extends vertically from the valve within the interior of the tank car and passes through an opening in the top of the tank car where the operating rod is rotatably sealed with respect to the tank car so as to permit rotation of the operating rod and the valve member, but so as to prevent leakage of the fluid lading carried by the tank car. As is shown in FIG. 2 of the drawings of the instant specification, prior art outside unloading devices typically included a length of pipe or a sleeve in communication with an opening in the tank car directly above the bottom mounted outlet valve. The operating rod or shaft extended upwardly through this sleeve and was sealed relative to the sleeve by means of a conventional packing seal carried by a packing box on the upper end of the sleeve. The upper end of the operating rod was typically of square or hexagonal cross section so that an operating wrench or handle may be applied thereto, thereby to enable an attendant standing on a platform (not shown in FIG. 1) to readily turn the operating rod so as to open or close the bottom outlet valve, as desired.
While the above-described prior art arrangement for outside unloading devices has worked well for a long period of time, certain long-standing problems have nevertheless existed. First, it will be appreciated that the length of the operating rod from its connection with the bottom outlet valve to the packing seals is rather long. For example, a typical interior diameter for a general service bottom slope tank car may be about 109.6 inches (2.78 m.). Additionally, such tank cars are often insulated so that the above-noted sleeve must extend upwardly from the exterior of the tank car through the insulation blanket and through the insulation shroud or shell. Even though the lower end of the operating rod is connected to the valve above the bottom of the tank car, the distance from the lower end of the connecting rod to the packing seals may typically be about 9-10 feet (2.7-3.1 m.).
It will be further appreciated that during fabrication of the car, due to possible mismeasurements of the opening in the bottom of the car for receiving the outlet valve and of the placement of the opening in the top of the car for the outside unloading device, and due to welding distortions and other distortions of the tank car body, as may be experienced during stress relieving operations, the axis of the packing seals may not be centrically aligned with the axis of the bottom mounted valve. Generally, the adequacy of the packing seal relative to the shaft was highly dependent on the alignment achieved between the bore of the packing housing or box and the operating rod. Such misalignments between the outlet valve and the packing box have resulted in leakage around the operating shaft and the packing material.